2561969981 has 2 divisors, whose sum is σ = 2561969982. Its totient is φ = 2561969980.

The previous prime is 2561969957. The next prime is 2561969999. The reversal of 2561969981 is 1899691652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1860196900 + 701773081 = 43130^2 + 26491^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2561969981 is a prime.

It is a super-2 number, since 2×2561969981² = 13127380367090280722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2561969951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1280984990 + 1280984991.

It is an arithmetic number, because the mean of its divisors is an integer number (1280984991).

Almost surely, 2^2561969981 is an apocalyptic number.

It is an amenable number.

2561969981 is a deficient number, since it is larger than the sum of its proper divisors (1).

2561969981 is an equidigital number, since it uses as much as digits as its factorization.

2561969981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2099520, while the sum is 56.

The square root of 2561969981 is about 50615.9064030271. The cubic root of 2561969981 is about 1368.3315653014.

The spelling of 2561969981 in words is "two billion, five hundred sixty-one million, nine hundred sixty-nine thousand, nine hundred eighty-one".